The present invention relates to a system for processing the surface of a target substrate by utilizing a gas in accordance with, e.g., film formation, etching, surface modification, impurity doping, or cleaning (removal of contaminants stuck to the surface), and a method of using the same. In other words, the present invention relates to a system for subjecting a target substrate to semiconductor processes, and a method of using the same. The term xe2x80x9csemiconductor processxe2x80x9d used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
Semiconductor processes using a reactive gas are widely used in the semiconductor manufacturing technology, e.g., CVD, surface modification, cleaning, and impurity doping, as well as etching. They are also often used in applications other than those employed in direct wafer processes, as in dry cleaning of a process chamber, and dry cleaning of an excimer laser exciting chamber or of the interior of the lens barrel of an electron beam exposure unit.
In semiconductor processes, in addition to harmful gases having high reactivity, many stable gases called PFCs (perfluorocarbons), which are believed to accelerate global warming, are also used. Although PFCs has a smaller production and a smaller exhaust amount than those of CO2, it has a larger relative influence as it has a very high global warming coefficient. For this reason, from the viewpoint of global environment protection, release of PFCs to the atmosphere must be eliminated. Many harmful gases used in semiconductor manufacture are released to the atmosphere without being processed, causing acid rain and environmental destruction. Recently, a detoxifying unit which removes exhaust gases by adsorption using zeolite or active carbon is used. However, the used adsorbent is incinerated or buried, which still imposes a heavy long-term load to the environment.
Various types of methods have been proposed for collection of PFCs. According to one example, exhaust gases filtered by the detoxifying unit are stored in a gas tank once and are transferred to a gas cylinder. The gas cylinder is transported to a gas refining factory, and the filtered exhaust gases are refined and reclaimed. As an in-line collection technique, a membrane having molecular-level fine pores is used to separate PFCs by utilizing the difference in molecular size between PFCs and a diluent gas such as nitrogen gas, thereby selectively collecting PFCs.
The former technique requires.a large-scale gas collection system, which is ineffective in terms of cost unless the same gas is used in a large amount. As semiconductor devices become more advanced, the gases used in semiconductor processes are altered often. Besides, in practice, the types of gas used for the processes vary very widely.
Since the latter technique utilizes a membrane, it is subjected to many limitations concerning the pressure of the gas supplied to the membrane and the concentration of the PFC gas with respect to the diluent gas. Accordingly, in a factory that processes a large amount of gas while arbitrarily repeating ON/OFF of the gas at the respective production units, the supply amount of exhaust gas is very unstable. It is almost impossible to run such a system as an in-line system (wherein the exhaust lines of many units are gathered and the exhaust gases are directly supplied to the separation unit).
FIG. 9 is a block diagram showing a conventional semiconductor wafer plasma etching system.
Referring to FIG. 9, in an etching process chamber 1, an Si wafer as a target substrate is placed on a susceptor. A reactive gas plasma is generated in the process chamber 1 to process a silicon oxide film on the wafer surface. As the etching gas, a gas mixture of C4F8/CO/Ar is used. C4F8 gas is regarded as a type of PFC gas and its exhaust amount will be regulated in the future. However, in semiconductor processes, a gas containing CF (fluorocarbon), e.g., C4F8, CF4, or CHF3, is indispensable. Therefore, in the semiconductor process field, efforts must be made to suppress the exhaust amount of CF-containing gases.
A gas mixture, the flow rates and mixing ratios of the respective gases of which are controlled, is introduced to the process chamber 1 through a gas supply line 2. The gas causes electric discharge due to an energy such as an RF (Radio-Frequency) power applied to an electrode provided in the process chamber 1, an RF power or microwave supplied from an external coil or antenna, to generate a gas plasma. Active species (F, CFx or the like having high reactivity) generated by this gas plasma are supplied to the surface of the SiO2 film. Chemical reaction progresses by the energy of ions that come from the plasma and bombard the wafer surface, and etching progresses as a reaction product having a high vapor pressure is produced. Accordingly, gases not decomposed in the plasma, decomposed gases such as F and CFx, gases such as COFx and CxFy generated by reactions of decomposed gases, and etching product gases such as SiFx (x=1 to 4) and CO2 generated by reactions with the etched film, are exhausted from the process chamber 1.
The gases exhausted from the process chamber 1 to an exhaust line 3 are evacuated by a turbo molecular pump (TMP) 4 serving as a vacuum exhaust unit, and a dry pump 5 arranged downstream the turbo molecular pump 4. The exhaust gases undergo a process of removing harmful substances by a detoxifying unit 13, flow through a duct in the factory to further remove solid matter with a scrubber, and are released into the atmosphere. The detoxifying unit 13 removes active and harmful F, COFx, CxFy, and the like, or harmful CO and the like by adsorption or combustion. Stable C4F8 gas passes through the detoxifying unit 13 without being removed and is finally released into the atmosphere, partially contributing to global warming.
According to the conventional collection method, a membrane filter or trap is provided at the output of the scrubber before the final stage, i.e., at the gathered exhaust lines of many units among the factories, so that the gases are separated and collected. With this method, the load on the collection system constantly varies in accordance with a change in operation states of the units, greatly decreasing the collection efficiency. A large amount of purging nitrogen is flowed to the exhaust system, e.g., the dry pump, of each unit in order to dilute harmful reactive gases, so that corrosion and degradation of the pump are suppressed. Hence, the CF-based gas concentration in the gas supplied to the collection system is diluted to less than 0.2% to further decrease the collection efficiency.
In this manner, with the conventional system or method, it is difficult to efficiently collect PFC gas and the like exhausted from the process chamber and the like at a low cost.
The present invention has been made in order to solve the conventional problems described above, and its object is to provide a semiconductor processing system which can efficiently collect PFC gas exhausted from a process chamber at a low cost.
According to a first aspect of the present invention, there is provided a semiconductor processing system comprising: a process chamber for accommodating a target substrate; a support member for supporting the target substrate in the process chamber; a gas supply mechanism for supplying a process gas into the process chamber; an exhaust mechanism for exhausting an interior of the process chamber, the exhaust mechanism having an exhaust line for flowing an exhaust gas, including fluorocarbon gas, from the process chamber; a trap capable of trapping the fluorocarbon gas in the exhaust gas by cooled adsorption and releasing the adsorbed fluorocarbon gas by heating; a regeneration line for releasing the adsorbed fluorocarbon gas from the trap while the trap is separated from the exhaust gas; a collection member connected to the regeneration line to collect the fluorocarbon gas released from the trap; a switching mechanism for switching modes of the trap between a trap mode in which the trap communicates with the exhaust line and a regeneration mode in which the trap communicates with the regeneration line; a cooling member for cooling the trap which is in the trap mode; and a heating member for heating the trap which is in the regeneration mode.
According to a second aspect of the present invention, there is provided a semiconductor processing system comprising: a process chamber for accommodating a target substrate; a support member for supporting the target substrate in the process chamber; a gas supply mechanism for supplying a process gas into the process chamber; an exhaust mechanism for exhausting an interior of the process chamber, the exhaust mechanism having an exhaust line for flowing an exhaust.gas, including fluorocarbon gas, from the process chamber; first and second traps capable of trapping the fluorocarbon gas in the exhaust gas by cooled adsorption and releasing the adsorbed fluorocarbon gas by heating; a regeneration line for releasing the adsorbed fluorocarbon gas from the first and second traps while the first and second traps are separated from the exhaust gas; a collection member connected to the regeneration line to collect the fluorocarbon gas released from the first and second traps; a switching mechanism for alternately switching the first and second traps between a trap mode in which one of the first and second traps communicates with the exhaust line and a regeneration mode in which the other of the first and second traps communicates with the regeneration line; a cooling member for cooling said one of the first and second traps which is in the trap mode; and a heating member for heating the other of the first and second traps which is in the regeneration mode.
According to a third aspect of the present invention, there is provided a method of using the semiconductor processing system of the second aspect, the method comprising: a first trapping step of trapping the fluorocarbon gas in the exhaust gas with the first trap; a first regeneration step of regenerating the second trap, in synchronism with the first trapping step, by releasing the adsorbed fluorocarbon gas from the second trap; a second trapping step of trapping the fluorocarbon gas in the exhaust gas with the second trap; and a second regeneration step of regenerating the first trap, in synchronism with the second trapping step, by releasing the adsorbed fluorocarbon gas from the first trap; wherein the first trapping and regeneration steps and the second trapping and regeneration steps are alternately switched.
According to the present invention, since traps are mounted along the exhaust line, PFC gas can be trapped before, for example, it is diluted very much, and can be collected efficiently at a low cost. While a trap that has trapped PFC gas is retreated and regenerated, a trap that has been regenerated is set along the exhaust line to replace the retreated trap. Therefore, it can trap and collect the gas efficiently.
According to the present invention, a means for introducing a gas, which has passed through the traps provided to the exhaust line, to the process chamber again may be further provided. If a reintroducing means is provided in this manner to recycle the gas, not only removal of harmful gases but also recycling of the gas is enabled, and the burden to the environment that accompanies gas manufacture and harmful gas removing process can be reduced greatly. When harmful gases are removed by adsorption with an adsorbent such as zeolite, the used absorbent must be processed. Either incineration or burial of the used absorbent brings about much burden on the environment.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.